LED modules in which InGaN chips and InGaAlP chips are combined are known. One exemplary application is a combination of phosphor-converted InGaN chips that emit mint-colored light (blue LED chip with (yellow-)green phosphor) together with InGaAlP chips that emit amber-colored light, for generating warm-white mixed light with high color rendering. Such LED modules are also known as “brilliant mix”, e.g. from a company publication from Osram Opto Semiconductors: “Brilliant Mix—Professional White for General Lighting”, January 2011. The “brilliant mix” is also described for example in DE 10 2009 047 789 A1 or WO 2011/044931 A1.
Between room temperature (25° C.) and a normal operating temperature (junction temperature) of approximately 80° C. to 100° C., a light power of the amber-colored InGaAlP chip decreases by typically 30% to 40%, while that of an InGaN chip decreases only by typically 5% to 20%. Overall, the mixed light may thus undergo a color change which is clearly perceptible to an observer and which may typically encompass up to 20 MacAdam steps. If, specifically, a “brilliant mix” LED module is set such that the color locus is situated on the Planckian locus at normal operating temperature, then the color locus shifts distinctly into the red in a cool state, e.g. when the LED module is switched on. This shift of the color locus (“color shift”) is undesirable, however.
EP 1 348 318 B1 discloses as a solution, in order to reduce the temperature-dependent shift of the cumulative color locus, an external regulation of the electrical operating currents through the LED chips, whereby the brightness thereof is regulated. In that case it is necessary either to measure the temperature and/or the color locus of the LED chips and then to correspondingly readjust the ratio of the operating currents through the InGaN and InGaAlP chips. This regulation is comparatively complex and expensive.